Many electronic devices comprise a circuit board and one or more electrical components having conductor feet protruding through holes of the circuit board. The holes of the circuit board are lined with electrically conductive sleeves that have galvanic contacts with appropriate other electrical conductors of the circuit board. The conductor feet of the electrical components are connected to electrical conductors of the circuit board by soldering so that the holes of the circuit board are at least partially filled with soldering material. The soldering can be carried out, for example, as a wave soldering where a wave of molten soldering material is arranged to sweep the side of the circuit board opposite to the side where of the electrical components are located.
In order to provide a reliable solder joint between a conductor foot of an electrical component and an electrically conductive sleeve in a hole of a circuit board, the temperatures of both the conductor foot and the electrically conductive sleeve have to be high enough when the molten soldering material is let to be absorbed into the hole of the circuit board. Otherwise there is a considerable risk for a forming a faulty “cold” solder joint. An inherent challenge related to the soldering is constituted by the thermal conductivity of the electrical conductors of the circuit board because temperature gradients in the electrical conductors tend to flatten, and this phenomenon lowers the temperature of the electrically conductive sleeve which is in contact with the soldering material. Typically, this problem is pursued to be solved by arranging the electrical conductors connected to the electrically conductive sleeve to form narrow isthmuses which are connected to the electrically conductive sleeve so as to decrease the heat conduction from the electrically conductive sleeve. However, these isthmuses must not be too narrow and/or too long because narrowing and/or lengthening the isthmuses increases electrical resistances between the electrically conductive sleeve and the one or more electrical conductors connected to the electrically conductive sleeve. Thus, there is an inherent trade-off between the thermal conductivity and the electrical resistances, and thereby there is a need for new technical solutions for providing reliable solder joints.